The colors are obviously much different. I thought that perhaps the alloys could be different, but I've seen this problem before. Below is a photo of a gun I did before the Geo, and I has the same issue. The dye was extremely fast striking, and I had a hard time getting a light color. It also had a strange reddish tint to it, unless I went REALLY dark.
I also noticed the buffer tube seems to look different under different light sources, while the Geo does not (see following posts). I really like the grey I got on my Geo, but I'm confused as to why it would be so different from use to use (dark, then light the next time, then dark again). Thoughts?